Abstract 1506: Upregulation of Cardiac AT1 Receptor Signaling Inhibits Myocyte Contractile Performance, [Ca2+]i Transient, and Ca2+ Current in Alcoholic Dogs: Insights into the Underlying Molecular Mechanism
Background. Chronic alcohol ingestion is accompanied by sustained renin-angiotensin system (RAS) activation followed by progressive left ventricular (LV) myocyte dysfunction. This suggests a role for angiotensin II (AII) in the development of alcoholic cardiomyopathy (ACM). We tested the hypothesis that chronic alcohol intake may cause upregulation of AII AT1 receptors and altered cardiac inotropic response to AII stimulation, thus contributing to the development of ACM.
Methods. We compared LV myocyte AT1- and AT2-receptor mRNA and protein levels, myocyte contractile function, [Ca2+]i transients ([Ca2+]iT), and Ca2+ current (ICa,L) in response to AII (10−6 M) in 16 instrumented dogs over 6 months. Eight animals received alcohol (once per day orally, providing 33% of total daily caloric intake), and eight were controls. Myocytes were isolated from LV myocardial biopsy tissues.
Results. Compared with controls, the alcoholic myocytes showed increased AT1 mRNA (0.69 vs 0.33) and protein levels (0.79 vs 0.37) (p<0.01). Conversely, AT2 mRNA (0.18 vs 0.16) and protein concentration (0.16 vs 0.14) were relatively unchanged. Importantly, in alcoholic myocytes, the increased AT1 receptors were associated with altered myocyte inotropic response to AII. In control myocytes, superfusion of AII (10−6 M) increased myocyte systolic amplitude (SA, 14.9 vs 12.4%) and the maximum rate of shortening (dL/dtmax, 203.1 vs 153.9 μm/s) accompanied by significant increases in [Ca2+]iT (1.52 vs 1.21) and ICa,L (4.0 vs 3.3 pA/pF). In alcoholic myocytes, this positive response was reversed. AII caused significant decreases in SA (3.4 vs 5.8 %), dL/dtmax (50.5 vs 78.9 μm/s), and the maximum rate of relaxation (dR/dtmax, 37.5 vs 59.6 μm/s) associated with reduced [Ca2+]iT (0.86 vs 1.12) and ICa,L (1.5 vs 2.1 pA/pF) (p<0.05). These AII-induced changes in alcoholic myocytes were abolished by incubation of alcoholic myocytes with an AT1 receptor blocker, losartan (10−5 M), or pretreatment with a Gi inhibitor, PTX (2 μg/ml, 36°C, 5h).
Conclusions. In a canine model, chronic alcohol consumption produces upregulation of LV myocyte AII AT1 receptors and alters myocyte functional response to AII stimulation, which may promote the development of ACM.